Since it is obligation to treat raw water for tap water by chlorination, the tap water after the treatment contains a certain amount of residual chlorine. Whereas, such residual chlorine has, beside a bactericidal action, an effect of oxidative decomposition of organic matters and generates organic halogen compounds such as trihalomethanes that are carcinogens. Such organic halogen compounds remaining in tap water have small molecular weights, and concentrations thereof in the tap water are very low. Thus, it has been difficult for conventional activated carbon to remove these organic halogen compounds sufficiently.
In order to solve this problem, optimization of pore diameter distribution of the activated carbon has been proposed. Conventionally, it has been thought that increase of a mesopore volume ratio is effective for the adsorption of such organic halogen compounds, so that various proposals have been offered.
For example, as activated carbon that is suitable for removing musty odor and trihalomethane, Patent Document 1 discloses activated carbon, of which a specific surface area of pores having diameters of 20 Å or more is 30 m2/g or more and 2500 m2/g or less, and a specific surface area of pores having diameters of less than 20 Å is 600 m2/g or more and 2500 m2/g or less. Also, as a method for manufacturing such activated carbon, a method including: mixing an organometallic compound such as a yttrium compound, a titanium compound and a zirconium compound with an activated carbon precursor in solvent; and performing carbonization treatment and activation treatment to the obtained mixture is disclosed.
Moreover, Patent Document 2 discloses a method for manufacturing activated carbon which adsorbs and removes trihalomethane precursors having comparatively high molecular weights (molasses and the like), and specifically discloses a method for modifying carbonaceous fiber, which includes: performing hydrophilic treatment to the carbonaceous fiber having a specific surface area of 0.1 m2/g to 1200 m2/g with an oxidant; and subsequently allowing the carbonaceous fiber to support alkali earth metal so as to perform activation treatment.
Furthermore, it has been thought that, in order to improve adsorption performance of activated carbon in dynamic adsorption under a water conducting condition, increase in contact efficiency between an adsorbate and micropores is effective. As a means for increasing the contact efficiency, various techniques for controlling mesopores which serve as introduction pores into the micropores have been proposed.
For example, Patent Document 3 discloses an organic halogen compound-removing filter, which is obtained by performing heat treatment to a mixture of; fibrous activated carbon of which a specific surface area of mesopores having pore diameters of 20 Å or more and less than 500 Å ranges from 100 m2/g to 2500 m2/g, a specific surface area of micropores having pore diameters of less than 20 Å ranges from 600 m2/g to 2500 m2/g, and a ratio of a mesopore volume with respect to a total pore volume ranges from 10% to 40%; and heat-fusible fiber, the organic halogen compound-removing filter being made of a molded body having apparent density of 0.25 g/cm3 to 0.60 g/cm3. Further, as a method for controlling the specific surface area, a manufacturing method including; mixing an organometallic compound (a yttrium compound, a titanium compound, a zirconium compound or the like) with an activated carbon precursor; and thereafter performing spinning fiber, infusibilization treatment, carbonization treatment and activation treatment is disclosed.
Moreover, Patent Document 4 discloses activated carbon, of which a mesopore volume in a range of pore diameters of 30 Å or more and less than 50 Å in pore diameter distribution that is obtained by a BJH method from a nitrogen adsorption isothermal line at 77.4 K ranges from 0.02 cc/g to 0.40 cc/g, and a ratio of the mesopore volume in the range with respect to a total pore volume ranges from 5% to 45%. As a method for controlling the pore volume, Patent Document 4 discloses a method for manufacturing activated carbon, in which a pitch containing 0.01% to 5% by weight of at least one kind of a metal component among Mg, Mn, Fe, Y, Pt and Gd is used as an activated carbon precursor, and the precursor is subjected to infusibilization treatment or carbonization treatment and activation treatment, wherein a mesopore mode diameter of the obtained activated carbon is controlled by varying the kind of the metal component.